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Free-triplet generation with improved efficiency in tetracene oligomers through spatially separated triplet pair states

Abstract

Singlet fission (SF) can potentially boost the efficiency of solar energy conversion by converting a singlet exciton (S1) into two free triplets (T1 + T1) through an intermediate state of a correlated triplet pair (TT). Although efficient TT generation has been recently realized in many intramolecular SF materials, their potential applications have been hindered by the poor efficiency of TT dissociation. Here we demonstrate that this can be overcome by employing a spatially separated 1(T…T) state with weak intertriplet coupling in tetracene oligomers with three or more chromophores. By using transient magneto-optical spectroscopic methods, we show that free-triplet generation can be markedly enhanced through the SF pathway that involves the spatially separated 1(T…T) state rather than the pathway mediated by the spatially adjacent TT state, leading to a marked improvement in free-triplet generation with an efficiency increase from 21% for the dimer to 85% (124%) for the trimer (tetramer).

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Fig. 1: Scenarios of the iSF processes involving different intermediate states.
Fig. 2: TA spectra revealing the iSF dynamics in the tetracene oligomers.
Fig. 3: MFE on the iSF dynamics in the tetracene oligomers.
Fig. 4: MFE on free-triplet generation in the tetracene oligomers.
Fig. 5: Solvent polarity effect on the iSF dynamics in the tetracene trimer.

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Data availability

The data shown in the paper are available from the figshare repository at https://doi.org/10.6084/m9.figshare.13669820.

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Acknowledgements

This work was supported by the National Key R&D Program of China (2017YFA0303703 and 2018YFA0209100), the National Natural Science Foundation of China (21922302, 21873047, 91850105, 91833305, 21722302 and 21673109), Jiangsu Provincial Funds for Distinguished Young Scientists (BK20160019), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and the Fundamental Research Funds for the Central Universities (0204-14380126). C.Z. acknowledges financial support from the Tang Scholar programme. We thank X. Wu for technical assistance. We are grateful to the High-Performance Computing Center of Nanjing University for performing the numerical calculations in this paper on its blade cluster system.

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C.Z. and M.X. initiated the project. Z.W., R.W. and L.C. performed the optical experiments. H.L. and X.L. synthesized the molecules. C.Z., Z.W. and X.W. analysed the data. Y.X., H.M., X.X., W.F. and Y.Y. performed the quantum chemical calculations. C.Z., Z.W. and M.X. co-wrote the manuscript with help from all the other authors.

Corresponding authors

Correspondence to Chunfeng Zhang, Haibo Ma, Xiyou Li or Min Xiao.

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Wang, Z., Liu, H., Xie, X. et al. Free-triplet generation with improved efficiency in tetracene oligomers through spatially separated triplet pair states. Nat. Chem. 13, 559–567 (2021). https://doi.org/10.1038/s41557-021-00665-7

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